Composition for equalizing radial and lateral force variations at the tire/road footprint of a pneumatic tire

ABSTRACT

A composition or particle mixture ( 20 ) for equalizing radial and lateral forces at the tire/road footprint of a pneumatic tire ( 11 ) due to tire/wheel assembly imbalance, non-uniformity of the tire, temporary disturbances in the road surface, or other vibrational effects of the unsprung mass of a vehicle whereby the particle mixture ( 20 ) is inserted into the interior of the tire ( 11 ). The composition is a dry solid particle mixture ( 20 ) wherein the particles are freely flowable and non-tacky at elevated tire temperatures, the particle mixture ( 20 ) is essentially devoid of liquid material, and the particle mixture ( 20 ) comprises two or more sets of particles wherein each set consists essentially of particles of a predetermined size or size range. The particle mixture ( 20 ) exhibits a multimodal particle size distribution.

This application claims the benefit of 60/133,775, filed May 12, 1999.

FIELD OF THE INVENTION

This invention relates to reducing disturbances in the unsprung mass ofa passenger car or light truck and particularly to a composition orparticle mixture for equalizing radial and lateral forces at thetire/road footprint of a pneumatic tire of a passenger car or lighttruck due to tire/wheel assembly imbalance, non-uniformity of the tire,temporary disturbances in the road surface, or other vibrational effectsof the unsprung mass of a vehicle.

BACKGROUND OF THE INVENTION

A typical motor vehicle is generally characterized as comprising anunsprung mass and a sprung mass. The unsprung mass generally consists ofall of the parts of the vehicle not supported by the vehicle suspensionsystem such as the tire/wheel assembly, steering knuckles, brakes andaxles. The sprung mass, conversely is all of the parts of the vehiclesupported by the vehicle suspension system. The unsprung mass can besusceptible to disturbances and vibration from a variety of sources suchas worn joints, misalignment of the wheel, brake drag, irregular tirewear, etc. Because vehicular tires support the sprung mass of a vehicleon a road surface and such tires are resilient, any irregularities inthe uniformity or dimensions of the tire, any dimensional irregularitiesin the wheel rim, and/or any dynamic imbalance or misalignment of thetire/wheel assembly will cause disturbances and vibrations to betransmitted to the sprung mass of the vehicle thereby producing anundesirable vehicle ride, as well as reducing handling and stabilitycharacteristics. Severe vibration can result in dangerous conditionssuch as wheel tramp or hop and wheel shimmy (shaking side-to-side).

It is now standard practice to reduce some of these adverse vibrationaleffects by balancing the wheel rim and tire assembly by using a balancemachine and clip-on lead weights. The lead balance weights are placed onthe rim flange of the wheel and clamped in place in a proper position asdirected by the balancing machine. The balancing procedure can reduceimbalance in the tire/wheel assembly, however, perfect balance is rarelyachieved. Balancing is not an exact art and the results are dependentupon the specific set up of a tire/wheel assembly on a specific balancerat that moment in time. Balancing is an improvement and will reduce thevibration of the tire/wheel assembly in comparison to an unbalancedtire/wheel assembly. However, even perfect balancing of the tire/wheelassembly does not necessarily mean that the tire will roll smoothly. Thebalancing of the tire/wheel assembly must necessarily be done in anunloaded condition. When the balanced tire is placed on the vehicle, theweight of the vehicle acts on the tire through the interface or contactarea of the tire and the road surface which is commonly known as thetire footprint. Irregularities in the tire are common such that even aperfectly balanced tire can have severe vibrations due tonon-uniformities in the tire which result in unequal forces within thetire footprint.

A level of non-uniformity is inherent in all tires. In the art ofmanufacturing pneumatic tires, rubber flow in the mold or minordifferences in the dimensions of the belts, beads, liners, treads, pliesof rubberized cords or the like, sometimes cause non-uniformities in thefinal tire. When non-uniformities are of sufficient magnitude, they willcause force variations on a surface, such as a road, against which thetires roll and thereby produce vibrational and acoustical disturbancesin the vehicle upon which the tires are mounted. Regardless of the causeof the force variations, when such variations exceed the acceptableminimum level, the ride of a vehicle utilizing such tires will beadversely affected.

Non-uniformity is generally characterized as 1) radial runout or out ofroundness, 2) radial force variations, and 3) lateral force variationsor conicity. Radial runout is the deviation from perfect roundness ofthe outer circumference of the tire. For example, the beads of the tiremay be not exactly concentric relative to the axis of rotation of thetire or the tread may not be concentric with the beads. Radial forcevariation is the deviation from spindle load transmitted by a perfecttire during rotation. For example, radial force anomalies in a tire mayresult from “hard” and/or “soft” spots in the tire due to structuralnon-uniformities such as inconsistent wall thickness, ply turn-upvariations, bead set, ply arrangement and other deviations. Lateralforce variation is the deviation from straight tracking during rotationof the tire. For example, lateral force variations can result if thebelt package of the tire is axially displaced or conically shaped. Whilelateral force variations will tend to pull the vehicle to a side of theroad, it is primarily the radial force variations, including radialrun-out, resulting in the vibration and acoustical effects which degradethe ride of the vehicle.

In a non-uniform tire, the radial run-out, the radial forces, and thelateral forces exerted by the tire will vary or change during itsrotation. In other words, the magnitude and/or direction of the radialrun-out, and the radial and lateral forces exerted by the tire willdepend on which increment of its tread is contacting the surface.

Accordingly, methods have been developed to correct for excessive forcevariations by removing rubber from the shoulders and/or the centralregion of the tire tread by means such as grinding. These methods arecommonly performed with a force variation or uniformity machine whichincludes an assembly for rotating a test tire against the surface of afreely rotating loading drum. This arrangement results in the loadingdrum being moved in a manner dependent on the forces exerted by therotating tire whereby forces may be measured by appropriately placedmeasuring devices. A computer interprets the force measurements andgrinders controlled by the computer remove rubber from the tire tread.However, grinding of the tire has certain disadvantages. For example,grinding can reduce the useful tread life of the tire, it may render thetire visually unappealing or it can lead to the development of irregularwear when the tire is in service on a vehicle.

While uniformity machines have been relatively successful in reducingthe undue vibrations transmitted to the sprung mass of the vehicle bythe tires, their complexity, manufacturing cost, and the requirement oftrained operating personnel has limited the use of these devicesprimarily to the manufacturing facilities of the vehicle tiremanufacturing companies. This has resulted in improved ridecharacteristics with respect to the original equipment tires on thevehicle but has done little to maintain the original improved ridecharacteristics when these original equipment tires are worn or replacedwith after market replacement tires. Further, the methods used inuniformity testing usually mount the tire on an axle or arbor fortesting rather than on the vehicular wheel rim. Because the wheel rimitself can have dimensional inaccuracies which affect uniformity and theremainder of the unsprung mass of the vehicle can also adversely affectuniformity characteristics, correcting the tires with force variationtire grinding without the tire being mounted on the wheel rim andvehicle on which it is to be used will fail to compensate for the totalirregularities of the tire/wheel assembly. Furthermore, thesecharacteristics can change as the tire is worn due to uneven orirregular wear and also normal wear progression.

Balancing of the tires has also been accomplished by using methods otherthan balance machines and lead weights. For example, Fogal in U.S. Pat.No. 5,073,217 disclosed a method of balancing a vehicle tire/wheelassembly by introducing a pulverulent synthetic plastic material intothe interior chamber of the tire wheel assembly. The pulverulentsynthetic plastic material has the added effect of compensating for theradial and lateral force variations generated at the tire roadinterface. The movement of the pulverulent synthetic plastic materialwithin the tire is proportional to the downward force of the vehicleweight and the centrifugal force due to the tire rotation. While theinvention disclosed in U.S. Pat. No. 5,073,217 worked effectively ontruck tires having a large gross vehicle weight (GVW), the 20–40 meshsize pulverulent synthetic plastic material was found to not work aseffectively for passenger type vehicles. The reason for the differentperformance is that the passenger vehicles have a significantly lowerGVW. The movement of the inserted particles is directly related to thedownward force on the tire. The weight of a typical passenger vehicle isnot sufficient to move the 20–40 mesh size pulverulent synthetic plasticmaterial properly within the passenger tire and was thus unable toeffectively equalize the radial and lateral forces.

Therefore, there remains a need in the art for an improvement inreducing radial and lateral force variations at the tire footprint duenot only to tire/wheel assembly imbalance, but reducing these forcevariations beyond the improvement levels available by balancing withonly conventional balancing methods, in a manner reducing forcevariations from other causes as well.

SUMMARY OF THE INVENTION

An object of this invention is to overcome the deficiencies anddisadvantages of the prior art, and provide a flowable material forcompensating for, and reducing vibrations caused by radial and lateralforces at the tire/road footprint of a pneumatic tire due to tire/wheelassembly imbalance, non-uniformity of the tire, temporary disturbancesin the road surface, or other vibrational effects of the unsprung massof a vehicle.

A further object of this invention is to enable effective compensationof such radial and lateral force variations on a continuous basis duringoperation of a vehicle and to extend the tread life of the vehicle tire.

The flowable material of the present invention comprises dry, solidparticle mixtures in which the particles are freely flowable andnon-tacky at temperatures of up to at least 150° C. (300° F.), and inwhich particle size distribution is multimodal (or polymodal), as willbe discussed in greater detail below. Compositions or particle mixturesaccording to this invention are those in which this particle sizedistribution is such as to be suitable for correcting tire imbalance andnon-uniformities of a tire/wheel assembly.

The preferred particle mixture consists of smaller particles than thosetested in U.S. Pat. No. 5,073,217. In an alternate embodiment theparticle mixture is supplemented by talc which lubricates the tireinnerliner surface and the individual particles of the particle mixture.The talc also acts as an anti-agglomeration agent to keep particlesseparate and freely flowing. The increased lubricity and smallerparticle size result in decreased response time for movement of theparticle mixture and also allows the particle mixture to properlydisperse under the lower vehicle GVW condition of passenger cars andlight trucks.

Depending on characteristics of the assembly or vehicle (such as GVW),the nature, size and quantity of the particle mixture is determined, theunsprung mass of the vehicle, the tire-to-road impact forces theparticle mixture proportionately toward such areas to null or eliminateradial force variation and achieve load force equalization. In otherwords, an amount of the particle mixture is forced to areas opposite theimpact and load forces, both sidewall-to-sidewall across the footprintof the tread and, of course, circumferentially about the tire. In thisfashion irrespective of the specific load force at any point betweentire and surface, eventual continuous tire rotation and tire load forcevariation results in displacement of the particle mixture to minimizeradial and lateral force variations, thereby placing the tire/wheelassembly in a uniform and force equalized condition. The aforesaid forceequalizing is desirably achieved instantaneously, and in the preferredembodiment, the particle mixture is relatively light and thus “moves”rapidly under variable load forces. Furthermore, the talc and theparticle mixture are compatible with the tire innerliners to lubricateand thereby maintain or add resiliency to the innerliners.

With the above, and other objects in view that will hereinafter appear,the nature of the invention will be more clearly understood by referenceto the following detailed description, the appended claims and theseveral views illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a single wheel model of a vehicle showing the relationshipof the sprung mass and the unsprung mass;

FIG. 2 is a fragmentary side elevational view of a conventionaltire/wheel assembly including a tire carried by a rim, and illustrates alower portion or “footprint” of the tire tread resting upon and bearingagainst an associated supporting surface, such as a road;

FIG. 3 is an axial vertical cross sectional view of a conventional rearposition unsprung mass of vehicle including the tire/wheel assembly ofFIG. 2 and additionally illustrates the lateral extent of the footprintwhen the tire rests under load upon the road surface;

FIG. 4 is a cross sectional view of the tire/wheel assembly of FIG. 3during rotation, and illustrates a plurality of radial load forces ofdifferent variations or magnitudes reacting between the tire and theroad surface as the tire rotates, and the manner in which the particlemixture is forced in position in proportion to the variable radialimpact forces;

FIG. 5 is a graph, and illustrates the relationship of the impact forcesto the location of the particle mixture relative to the tire when underrolling/running conditions during equalizing in accordance with FIG. 4;

FIG. 6 is a graph of the balancing composition and illustrates theconcept of multimodality as described in the present invention; and

FIG. 7 is a graph similar to FIG. 6 and further illustrates the conceptof multimodality as described in the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is first made to FIG. 1 of the drawings which shows a singlewheel model of a vehicle where symbol Ms denotes the mass of a sprungvehicle structure (hereafter referred to as sprung mass) and Mu denotesthe mass of an unsprung structure (hereafter referred to as unsprungmass). The unsprung mass Mu generally consists of all of the parts ofthe vehicle not supported by the vehicle suspension system such as thetire/wheel assembly, steering knuckles, brakes and axles. The sprungmass Ms, conversely is all of the parts of the vehicle supported by thevehicle suspension system. Symbol Ks denotes the spring constant of avehicle spring, and Cs denotes the damping force of the shock absorber.The unsprung mass Mu can be susceptible to disturbances and vibrationfrom a variety of sources such as worn joints, misalignment of thewheel, brake drag, irregular tire wear, etc. The vehicular tires areresilient and support the sprung mass Ms of a vehicle on a road surfaceas represented by the spring rate of the tires as symbol Kt. Anyirregularities in the uniformity or dimensions of the tire can result ina variable spring rate Kt which, as the tire rotates, can causevibration of the unsprung mass Mu which is transmitted to the sprungmass Ms. In addition, any dimensional irregularities in the wheel rim,and/or any dynamic imbalance or misalignment of the tire/wheel assemblywill cause disturbances and vibrations to be transmitted to the sprungmass Ms of the vehicle thereby producing an undesirable or rough vehicleride, as well as reducing handling and stability characteristics of thevehicle.

Referring now to FIGS. 2 and 3 of the drawings which illustrate atire/wheel assembly 10, that is an element of the unsprung mass Mureferred to in FIG. 1. A tire 11 and a metal rim 12 carrying a tireinflation valve define the tire/wheel assembly 10. The tire 11 is aradial tire. A biased tire essentially does not flex radially whereas aradial tire tends to flex radially, and in use the latter can beevidenced by sidewalls SW1, SW2 (FIGS. 2, 3 and 4) which tend to bulgeoutwardly under load when resting or running upon a surface, such as aroad R. The amount of flex will vary depending upon such things as thetire construction, proper tire inflation, total load of the vehicle, thespeed of the vehicle, etc. and the load force can vary from wheelassembly to wheel assembly both in smaller passenger vehicles and largerpassenger vehicles, such as sports utility vehicles.

The radial tire 11 includes a lower tire portion or a footprint Bdefined by a length L and a lateral breadth or width W whichcollectively define the instantaneous cross sectional area of the tirefootprint B in engagement with the supporting surface or road R when thetire/wheel assembly 10 is stationary or is rotating. The tire T includesa conventional external tire tread T and beads B1, B2 of the respectivesidewalls SW1, SW2 which engage the rim 12 in a conventional manner.

If the tire/wheel assembly 10 and similar tire/wheel assembliesassociated with a vehicle (not shown) are not properly/perfectlybalanced, the attendant unbalanced condition thereof during vehiclewheel rotation will cause the tires to wear unevenly, wheel bearingswill wear excessively, shock absorbers operate at inordinately higheramplitudes and speeds, steering linkages/mechanisms vibrate excessivelyand become worn and overall vehicle ride is not only rough anddangerous, but also creates excessive component wear of the entirevehicle. As previously mentioned, even if the tire/wheel assembly 10 wasbalanced as perfectly as possible with lead weights, other problemsassociated with the unsprung mass Mu such as non-uniformities in thetire, drag from the brakes, worn linkages, changing road conditions,tire wear, vehicle weight changes, etc., can cause even the “perfect”balanced tire/wheel assembly 10 to have vibrational problems.Accordingly, balancing of the tire/wheel assembly can be replaced andenhanced by using the particle mixture inside the tire to balance radialand lateral force variations. Thus, as forces vary during rotation ofthe tire/wheel assembly 10 relative to the road R, these forces must beequalized and the response time for such force variation equalizationshould be virtually instantaneous irrespective of the tire-to-road forceand/or amplitude. It may be possible to balance the tire using astandard tire balance machine and lead weights in addition to using theimproved particle composition of the present invention. However, anygains in reduced radial and lateral force variations at the tirefootprint may be lost if the tire loses its balance due to wear or someother condition.

In keeping with the present invention, equalizing of radial and lateralforces at the tire/road footprint B of a pneumatic tire 11 due totire/wheel assembly imbalance, non-uniformity of the tire, temporarydisturbances in the road surface, or other vibrational effects of theunsprung mass Mu of a vehicle is accomplished by inserting an amount ofa particle mixture 20 into the interior of the tire 11 of the tire/wheelassembly 10. A predetermined amount/weight of the material 20 can beplaced in the interior I of the tire 11 prior to the tire 11 beingmounted upon the rim 12. However, it is also possible to inject theflowable material 20 into the tire interior I after the tire 11 has beenmounted on the rim 12, through the tire valve or air valve 13. Thisprocess is repeated with each tire of each tire/wheel assembly 10 of theparticular vehicle involved, and once completed the vehicle is thenmerely driven along the road R whereupon each tire/wheel assembly 10 isrotated and the force variations are equalized.

Reference is made to FIGS. 4 and 5 which illustrate the innumerableradial impact forces (Fn) which continuously react between the road Rand the tread T at the lower portion or footprint B during tire/wheelassembly rotation. There are an infinite number of such forces Fn atvirtually an infinite number of locations (Pn) across the lateral widthW and the length L of the footprint B, and FIGS. 4 and 5diagrammatically illustrate five such impact forces F1–F5 at respectivelocations P1–P5. As is shown in FIG. 5, it is assumed that the forcesF1–F5 are different each from each other because of such factors as tirewear at the specific impact force location, the road condition at eachimpact force location, the load upon each tire/wheel assembly, etc.Thus, the least impact force is the force F1 at location P1 whereas thegreatest impact force is the force F2 at location P2. Once again, theseforces F1–F5 are merely exemplary of innumerable/infinite forceslaterally across the tire 11 between the sidewalls SW1 and SW2 andcircumferentially along the tire interior which are created continuouslyand which vary as the tire/wheel assembly 10 rotates. As these impactforces are generated during tire/wheel assembly rotation, the particlemixture 20 relocates from its initial position in dependency upon thelocation and the severity of the impact forces Fn. The relocation of theparticle mixture 20 through movement of the individual granules, powderand dust is also inversely related to the magnitude of the impactforces. For example, the greatest force F1 (FIG. 5) is at position P1,and due to these greater forces F1, the particle mixture 20 is forcedaway from the point P1 and the least amount of the particle mixtureremains at the point P1 because the load force thereat is the highest.Contrarily, the impact force F is the lowest at the impact forcelocation point P2 and therefor more of the particle mixture 20 willremain thereat (FIG. 4). In other words, at points of maximum orgreatest impact forces (F1 in the example), the quantity of the particlemixture 20 is the least, whereas at points of minimum force impact(point P2 in the example), the quantity of particle mixture 20 isproportionately increased creating lift therefore equalizing the radialforce variations. Accordingly, the vibrations or impact forces Fn forcethe particle mixture 20 to continuously move away from the higher orexcessive impact areas F1 or areas of maximum imbalance F1 and towardthe areas of minimum impact forces or imbalance F2. The particle mixture20 is moved by these impact forces Fn both laterally andcircumferentially, but if a single force and a single granule of theparticle mixture 20 could be isolated, so to speak, from the standpointof cause and effect, a single granule located at a point of maximumimpact force Fn would be theoretically moved 180 degrees therefrom.Essentially, with an adequate quantity of particle mixture 20, thevariable forces Fn create through the impact thereof a lifting effectwithin the tire interior I which equalizes the radial force variationapplied against the footprint until there is a total force equalizationcircumferentially and laterally of the complete tire/wheel assembly 11.Thus the rolling forces created by the rotation of the tire/wheelassembly 10 in effect create the energy or force Fn which is utilized tolocate the particle mixture 20 to achieve lift and force equalizationand assure a smooth ride. Furthermore, due to the characteristics of theparticle mixture 20, road resonance is absorbed as the tire/wheelassemblies 10 rotate.

Referring now to the particle mixture 20, the compositions according tothe present invention are dry solid particle mixtures in which theparticles are freely stable, flowable and non-tacky at elevatedtemperatures typically achieved by a tire such as temperatures up to150° C. (300° F.). This temperature is above the highest operatingtemperature in a tire under normal conditions. The particle mixture isessentially devoid of liquid material, since the presence of liquidwould interfere with free movement or tumbling of particles which isessential in order to obtain proper force equalization. Any particulatematerial that is stable and remains free flowing over all conditions oftire usage, has a specific gravity greater than 1, and is available inthe particle sizes to be discussed below, can be used. An importantrequirement is that the particulate material must be more thermallystable than the tire in which it is used under all tire operatingconditions. Another characteristic of composition according to thisinvention is the particles comprising the composition should havehardness sufficient to withstand the repeating tumbling which will occurin an automobile tire without substantial abrasion.

A particle mixture according to this invention may consist essentiallyof particles which are of regular shape (e.g., spheres or ellipsoids),preferably regular size and shape; or particles of irregular size andshape, e.g., pulverulent material (granules, powder or dust); or whichmay comprise a mixture of the two.

Compositions or particle mixtures according to the present invention canhave a particle size distribution range which may be characterized asmultimodal or polymodal (e.g., bimodal, trimodal or tetramodal). Thatis, a plot of weight fraction vs. particle diameter will show two ormore particle sizes or particle size ranges having relatively highconcentration of particles, separated by a region of particle size rangein which there are no particles or few particles.

The particles according to the present invention are preferablypolymeric (plastic) although any material exhibiting the necessarycharacteristics outlined above may be used. Polymeric materials are forthe most part organic. Organic polymeric materials for the practice ofthis invention may be either homopolymers (polymers of one monomer) orcopolymers (polymers of two or more monomers). Polymeric materials maybe either thermoset or thermoplastic. Thermoset materials include ureaformaldehyde, melamine formaldehyde, phenolic, or epoxy, to name a fewof such materials. The thermoset resins described herein are availableas molding powders, which typically include a major amount of the resin,a minor amount of a filler or fillers, and optionally small amounts ofother ingredients. Suitable thermoplastics for particles according tothe present invention include nylon and polyester (e.g., polyethyleneterephthalate (or PET)). All of these materials are well known inparticle form. Thermoset materials are inherently dry and non-melting.Thermoplastic materials in accordance with the present invention arethose which have melting points (or softening points) above 150° C.(300° F.).

In addition to the particle mixture, an alternate embodiment of thepresent invention includes using a lubrication material such as talc asa supplement to the particle mixture. The talc coats the individualparticles which results in an increase in lubricity of the mixture andenables the particles to move faster and in response to less force. Thetalc also acts as an anti-agglomeration agent to keep particles separateand freely flowing. In addition, the talc lubricates the innerliner ofthe tire which provides additional lubricity for particle movement andthereby maintain or add resiliency to the innerliners. The amount oftalc used for passenger tires is preferably in a range of about 15–30%by weight of the amount of particle mixture inserted into the tire.

The composition according to a preferred embodiment of this inventionconsist essentially of particles (e.g., pulverulent material, which maybe powder or dust), wherein the particles size distribution ismultimodal. Such particle size distribution may be achieved, forexample, by combining two sets of particles, wherein a first setconsists essentially of particles in one size range (e.g., a coarsersize range) and a second set of particles consists essentially ofparticles in a second size range (e.g., finer particles). The particlesize distribution within each set of particle size range is typicallysuch that the set has a modal particle size (which may be expressedeither in terms of mesh or particle diameter) which represents the sizehaving the greatest concentration of particles. Typically this modaldiameter or size is somewhere in the middle of the size range, and thereis a relatively small concentration of particles at either boundary ofthe size range. Size ranges of two sets of particles may be eitheroverlapping or non-overlapping. When the size ranges of the two sets arenon-overlapping, there will be a virtually zero concentration ofparticles having sizes which are between the two ranges. When the sizeranges are overlapping, the overall mixture may exhibit two or morepeaks representing modal particle sizes in the two or more sets, withvalleys representing smaller concentrations of particles having sizeswhich are between the peaks. The zone of overlap (which is the particlesize range in which two sets of particles overlap) will have arelatively small concentration of particles.

Referring now to FIGS. 6 and 7, graphs are shown of typical multimodalcompositions. The graphs are a plot of weight fraction vs. particlediameter with both increasing with distance from zero point at the lowerleft side of the graph. FIG. 6 depicts a trimodal composition havingthree distinct particle diameter ranges 21, 22, and 23. The ranges arecentered about midpoint of the each range identified as 24, 25, and 26,respectively. Ranges 21 and 22 are shown to overlap at area 27. Althoughnot shown, areas of overlap may result in another smaller mode having apeak particle weight fraction at the point of intersection of theranges. Range 23 does not overlap with any other range.

FIG. 7 depicts a multi-modal composition having one non-overlappingparticle diameter range 31 and three overlapping particle diameter sizes32, 33, and 34. The ranges are centered about midpoint of the each rangeidentified as 35, 36, 37, and 38, respectively. While the particleweight fraction for each group was generally the same in FIG. 6, theparticle weight fraction of range 31 is significantly larger than thatof the other groups. Ranges 32, 33, and 34 are shown to overlap at areas39 and 40. There are innumerable combinations of modes having differentranges of diameters and different weight fractions. One embodiment ofthe invention uses a polymodal blend having particle sizes of 60, 80,100, 120, 240, 270 (U.S. mesh size) in which the weight percentages ofthe different sized particles are varied to optimize performance for aparticular application. The smaller particles act as a lubricant makingthe addition of a lubricant material unnecessary. FIGS. 6 and 7 are notintended to limit the present invention to any particular compositionmake-up, but merely to aid in the understanding of the concept of thepresent invention. The modality and weight percentages for a particularmaterial used in a particular make and size of tire on a particularvehicle can be adjusted experimentally to optimize the ability of thecomposition to balance the tire/wheel assembly.

Particle mixtures or compositions according to the present invention,having a multimodal particle size distribution, are highly advantageousfor force equalizing a wheel assembly, as compared to previously knownparticle blends or mixtures in which sizes of particles varycontinuously over the entire range or spectrum of sizes present. In aparticle mixture of the present invention, smaller particles move firstin response to smaller forces. The larger particles then move in asecond stage when forces are greater. The relative absence of particleshaving sizes between those of the smaller particles and those of thelarger particles appears to be advantageous in facilitating complete andrapid response to forces causing tire imbalance.

Smaller particles in compositions of the present invention will respondto smaller forces and move more quickly to a position opposite theforce. The larger particles add stability and react to larger forces.Compositions of the present invention respond to smaller forces than docurrent formulations for balancing wheel assemblies. The forcesencountered in a passenger or light truck tire are smaller than thoseencountered in larger tires, such as those used in trucks and airplanes.The compositions of the present invention fulfill a need forcompositions which will afford both the effects of dynamic balancing andthe equalization of radial and lateral force variations due to tirenon-uniformity for passenger and light truck tires. Particle mixturesaccording to this invention respond more rapidly and more completelythan do particle mixtures having a monomodal particle size distribution(i.e., a continuous spectrum of particle sizes ranging from a maximum toa minimum).

The optimum amount (or weight) of a particular particle mixture per tireto be used will vary over a wide range, depending on the size of thetire, the GVW, and amount of the tire is out of balance or otherfactors, whether this amount be expressed as a suitable range or as aoptimum amount. For example, the preferred amount for passenger andlight truck vehicles is in a range of 0.25–2.0 ounces while largervehicles may use a much larger amount. In addition, the optimum size orsize distribution of the particles in the composition will vary as well.Compositions with smaller particles are preferred for lighter weightvehicles as they will respond to smaller forces and move more quickly toa position opposite the force. The larger particles add stability andreact to larger forces. For example, a multimodal blend of particlesizes for passenger and light truck vehicles comprises particle sizes of60, 80, 100, 120, 240, 270 (U.S. mesh size) in which the weightpercentages of the different sized particles are varied to optimizeperformance for a particular application. Another blend uses particle ina range of 60–80 mesh size. Other preferred formulations includefiberglass particles of 140–170 mesh size while larger vehicles may usea larger range preferably about 20–40 mesh size. A table showing theexemplary amounts of 60–80 mesh size particle mix and talc for differenttire wheel sizes is shown below. The material amounts are given as anominal value with a plus or minus tolerance and the talc is given as arange and generally represents 20–30% of the material amount:

Exemplary Amount of 60–80 Mesh Size Pulverulent Synthetic PlasticMaterial and Talc for Passenger and Light Truck Tires TIRE WHEEL AMOUNTOF AMOUNT OF SIZE MATERIAL (oz.) TALC (oz.) 13″ 0.4 ± 0.2 0.1–0.2 14″0.7 ± 0.3 0.2–0.3 15″ 1.1 ± 0.4 0.2–0.4 16″ 1.3 ± 0.4 0.2–0.5 17″ 1.5 ±0.5 0.3–0.6

These amounts can also be used for a multimodal blend of 60, 80, 100,120, 240, 270 (U.S. mesh size), wherein the amount of talc is no longernecessary due to the small particles of the multimodal blend which actas a lubricant. The total amounts of the multimodal 60, 80, 100, 120,240, 270 can be increased to include the weight amount of the replacedtalc. In the 60, 80, 100, 120, 240, 270 blend, the weight percentage ofthe smaller particles, 240, 270 mesh, will generally correspond to theweight amount specified for talc when using the 60–80 blend.

The effectiveness of the present invention and the utilization of theparticle mixture to equalize force variations of a tire/wheel assemblieswas tested using an MTS Flat-Trac II® test machine. A GoodyearP225/60R16 Eagle LS tire was mounted on a 16×7.0 rim and inflated to 35psi. The tire was dual plane balanced and then run on the test machineat 70 mph and then at 80 mph under a 1200 lb. test load. The 1^(st)order radial and fore/aft forces were recorded during each run. The tirewas then single plane balanced and a quantity (q1) of the internalbalancing material of the present invention was inserted into the tire.The test conditions were then repeated at both 70 and 80 mph. The testwas repeated using a second quantity (q2) of the internal balancingmaterial of the present invention inserted into the tire. Both testquantities were in the recommended quantity range for a 16″ tire asdisclosed above. The material used was a pulverulent blend used was amultimodal blend having particle sizes of 60, 80, 100, 120, 240, 270U.S. mesh size. The results of the test are summarized below:

Test Results

Goodyear Eagle LS - P225/60R16 at 35 psi on MTS Flat-Trac II ® at 1200lbs. test load Radial First Order Force Fore/Aft First Order ForceVariation (pounds) Variation (pounds) Single Single Single Single PlanePlane Plane Plane Dual Balance Balance Dual Balance Balance Plane andand Plane and and Speed Balance Material Material Balance MaterialMaterial (MPH) Only q1 q2 Only q1 q2 70 10.4 7.5 5.8 21.4 17.5 12.1 8014.5 10.5 7.0 30.6 25.0 17.9

The test results show a significant improvement in the both radial andfore/aft force variations using the internal balancing material of thepresent invention. This results in an improved ride performance of thetire. The tire was also checked for a balance comparison where the tirewas run unloaded and the radial 1^(st) order force variation wasrecorded. The test results are below:

Goodyear Eagle LS - P225/60R16 at 35 psi on MTS Flat-Trac II ® at 0 lbs.test load Dual Plane Single Plane Single Plane Balance Balance andBalance and BALANCE TEST Only Material q1 Material q2 Radial First Order9.6 8.1 8.2 Force Variation (pounds)

While the test results show improvement in the balance of the tire. Thetest results also show that the improvement obtained is not just relatedto the improvement of the tire balance, but to the ability of theinternal balancing material of the present invention to equalize forcevariations when the tire is rotating under loaded conditions.

Although the present invention has been described above in detail, thesame is by way of illustration and example only and is not to be takenas a limitation on the present invention. Accordingly, the scope andcontent of the present invention are to be defined only by the terms ofthe appended claims.

1. A system for equalizing radial and lateral force variations at atire/road footprint of a pneumatic tire/wheel assembly comprising: apneumatic tire/wheel assembly; and a dry solid particle mixturepositioned within the tire/wheel assembly, wherein (a) the particlesforming said particle mixture are freely flowable and non-tacky attemperatures up to 150 degrees C.; (b) said particle mixture isessentially devoid of liquid material; (c) said particle mixturecomprises a plurality of sets of particles, wherein each set consistsessentially of particles of a predetermined size or size range; (d) saidparticle mixture exhibits a multimodal particle size distribution; and(e) said particles are in a size range substantially between 60–270 U.S.screen size.
 2. The system of claim 1, wherein said particle mixturecomprises spheres of a first diameter and spheres of a second diameter.3. The system of claim 1, wherein said particle mixture comprises afirst set of particles having a first size range and a second set ofparticles having a second size range, the particle size distribution ofsaid particle mixture being characterized by at least two peaks.
 4. Thesystem of claim 1, wherein said particle mixture comprises a first setof particles having a first size range, a second set of particles havinga second size range, a third set of particles having a third size range,wherein the particle sizes ranges do not overlap.
 5. The system of claim1, wherein said particles forming said particle mixture have a specificgravity greater than
 1. 6. The system of claim 1, wherein said particlesforming said particle mixture have sufficient hardness to prevent themfrom degrading while tumbling in said tire.
 7. The system of claim 1,wherein said mixture comprises polymeric resin particles.
 8. The systemof claim 7, wherein said particle mixture includes substantially 70% byweight of said polymeric resin and 28% by weight of a cellulosematerial.
 9. The system of claim 7, wherein said polymeric resin is athermoset material.
 10. A dry solid particle mixture for equalizingradial and lateral force variations at the tire/road footprint of apneumatic tire, wherein (a) the particles forming said particle mixtureare freely flowable and non-tacky at temperatures up to 150 degrees C.;(b) said particle mixture is essentially devoid of liquid material; (c)said particle mixture comprises a plurality of sets of particles,wherein each set consists essentially of particles of a predeterminedsize or size range; and (d) said particle mixture exhibits a multimodalparticle size distribution; and (e) said mixture comprises polymericresin particles wherein said polymeric resin is a thermoplasticmaterial.
 11. A dry solid particle mixture for equalizing radial andlateral force variations at the tire/road footprint of a pneumatic tire,wherein (a) the particles forming said particle mixture are freelyflowable and non-tacky at temperatures up to 150 degrees C.; (b) saidparticle mixture is essentially devoid of liquid material; (c) saidparticle mixture comprises a plurality of sets of particles, whereineach set consists essentially of particles of a predetermined size orsize range; and (d) said particle mixture exhibits a multimodal particlesize distribution; and (e) one set of particles is made of fiberglass.12. The particle mixture according to claim 11, wherein said fiberglassparticles are in a size range substantially between 130–200 U.S. screensize.
 13. The system of claim 1, further comprising a lubricantmaterial.
 14. The system of claim 13, wherein said lubricant particlesare in a size range substantially between 200–325 U.S. screen size. 15.The system of claim 13, wherein said particle mixture comprises 15–30%lubricant material by weight.
 16. The system of claim 13, wherein saidlubricant is talc.
 17. The system of claim 13, wherein said lubricant iscorn starch.
 18. The system of claim 13, wherein said lubricant is ananti-agglomeration agent.